8 - State Categories
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States are a powerful way to create expressive groups of variables. Some UI elements may require a combination of states to be applied simultaneously.
For example, consider a Button component which displays a button callout.
This button might be a standard Button with the following states:
Enabled
Disabled
Highlighted
Pushed
But it may also have states for which button icon to display:
A
B
X
Y
LeftStick
RightStick
These two sets of states could be set independently and combined at runtime. Categories let you create groups of states so that multiple states can be set simultaneously.
For this tutorial we'll create a new component. This component has state categories for size and for color. To do this:
Open Gum
Create a new Component called CategoryDemo
Right-click anywhere in the State box and select Add Category
Enter the name "Size" for the new category and click OK
Repeat the above steps to create a "Color" category
Now we can add states to the categories. To do this:
Right-click on the Size category and select Add State
Enter the name "Small" for the new state
Right-click on the Size category again and select Add State
Add a second state to "Big"
Right-click on the Color category and select Add State
Add a state called "Red"
Right-click on the Color category again and select Add State
Add a state called "Blue"
Now that we have states set up we need to add a visual element to the component so that we can see our changes.
To do this, select the Default state and drag+drop a ColoredRectangle into your component
To modify a state, you can select it and edit in the Editor tab or change properties in the Variables tab to modify what the state sets. Notice that normally for a component like this the ColoredRectangleInstance would have its width and height be relative to its container, but we're not doing this for the sake of keeping the tutorial shorter.
First we'll set the Size states. To do this:
Select the Big state
Resize the colored rectangle so it is larger than the default
Select the Small state
Resize the colored rectangle so it is smaller than the default
Next we'll set the Color states. To do this:
Select the Red state
Set the Red, Green, and Blue values to: 255, 0, 0
Select the Blue state
Set the Red, Green, Blue values to: 0, 0, 255
Now that we have our CategoryDemo component set up with multiple categories, we can view these states on any CategoryDemo instance. To do this:
Create a Screen called "CategoryDemoScreen"
Drop an instance of the CategoryDemo component into the CategoryDemoScreen
Select the newly-created CategoryDemoInstance
Scroll down in the Variables list and notice that the instance has drop-downs for each category.
You can set each state independently and the states combine
We can revert the states back to their unset values by right-clicking on the state variable and selecting the Make Default item.
If a variable is modified in one of the states in a category, then all of the states in that category are automatically assigned the default value, and this value is explicitly set. This concept makes working with states far more predictable.
For example, consider a component which has:
A single ColoredRectangle
A category called RectangleSizeCategory
States called Big, Medium, and Small
Initially, all states in a category do not explicitly assign any variables. We can see this by selecting the category and observing the Variables tab.
If a variable is changed in one of the states in the category, then that variable propagates to all other states, and the Category lists this as one of the variables that it modifies.
For example, we can select the Big category and change the ColoredRectangle.Width property to 150.
Once this value is changed, the RectangleSizeCategory lists this as a variable that it modifies in the Variables tab.
If we select any of the other states in the category, they show that they explicitly set the Width value as well (the value has a white background instead of light green). The value is inherited from the default state.
Once a variable is set in a category, all states are required to set this value. A variable cannot be removed from a single state in a category. Rather, to remove a variable, all states in the category must remove the variable. This can be done by selecting the category and pressing the X button next to the variable name.
